The present invention relates to a vertical heat treatment apparatus to be used in fabrication processes of objects to be fabricated, e.g., semiconductor devices, LCD substrates, etc.
A variety of conventional heat treatment apparatuses have been used in semiconductor fabrication processes. These fabrication processes include treatments, such as forming oxide films, forming thin films by thermal CVD, forming heavily doped regions, etc., on semiconductor wafers, LCD substrates, etc. The heat treatment apparatuses for these purposes have been conventionally of the horizontal type, but recently those of the vertical type are becoming dominant. In such a vertical heat treatment apparatus, a heat source, such as a heater, is provided on the upper surface or around a vertical processing vessel of, e.g., quartz, having an inverted U-shaped section. A loading mechanism, such as a wafer boat or others, is provided for loading objects to be treated, while held in a horizontal orientation, into the processing vessel from below the processing vessel, so that the objects to be treated are heated up to a required temperature in the processing vessel. Various heat treatments are then conducted on the objects to be treated with required gases fed into the processing vessel.
Higher precision of such heat treatments, higher treating efficiency, etc. are required of such vertical heat treatment apparatus to achieve homogeneous film quality and uniform film thicknesses in a plane of the objects to be treated. In addition, semiconductor processing is increasingly becoming more precision oriented, and the typical diameter of semiconductor wafers that are being treated has increased from 8 inches to 12 inches. The heat treating requirements associated with larger size substrates, such as LCD substrates, etc. are more exacting than those for smaller sized substrates. These requirements involve, for example, higher precision and higher efficiency in the heat treatments being made.
To meet these requirements, an important factor is how to heat and treat efficiently for a short period of time the objects to be treated that are loaded in the process vessels of the vertical heat treatment apparatus. An additional important factor is how to improve, in the heat treatment, the uniformity of temperature distributions in the place where the loaded objects are treated.
But in the conventional vertical heat treatment apparatus, objects to be treated are heated only by a heat source, e.g., a heater or the like, which is provided on the upper surface of the processing vessel or around the same and whose output is controlled to heat the objects to be treated by radiant heat. No additional means for achieving more homogeneous heating is provided. Accordingly, the above-described requirements cannot be met when treating large objects, such as large diameter semiconductor wafers, LCD substrates, etc. whose uniform temperature distribution in place cannot be achieved because the abrupt heating requirement presents difficulties in connection with maintaining the desired treating temperatures. For instance, disuniform temperatures partially occur in the circumferential direction of the objects to be treated, and temperature differences take place between the central parts of the objects to be treated and the peripheral parts thereof due to larger heat radiation amounts in the peripheral parts as compared with the central parts.